WESTON (dpa-AFX) - Biogen Inc. (BIIB) on Tuesday reported detailed results from the Phase 2 CELIA study of its experimental Alzheimer's disease treatment diranersen, showing the drug slowed clinical decline and reduced tau pathology in patients with early-stage disease.
The data, presented at the Alzheimer's Association International Conference 2026, expanded on previously disclosed topline results and provided Phase 2 proof of concept for diranersen's tau-targeting mechanism.
At 18 months, the 60 mg dose administered every six months produced the strongest results. Compared with placebo, the treatment slowed clinical decline by 26% on the Clinical Dementia Rating-Sum of Boxes (CDR-SB), 50% on the Mini-Mental State Examination (MMSE), 42% on ADAS-Cog13, 30% on the modified iADRS, and 23% on ADCOMS.
Biogen said diranersen is the first tau-directed therapy to demonstrate substantial reductions in both cerebrospinal fluid total tau and brain tau pathology in a Phase 2 study, with total tau levels declining by 50% to 65% across all doses evaluated.
As previously disclosed, the CELIA study did not meet its primary endpoint, which was designed to determine whether higher doses of diranersen would provide greater clinical benefit based on dose response on the CDR-SB scale at 18 months. A clear dose-response relationship was not observed in the study.
Based on the combined Phase 1b and Phase 2 data, Biogen plans to advance diranersen into Phase 3 development.
'The CELIA data provide some of the clearest evidence that reducing tau pathology can translate into clinically meaningful benefit,' said Professor Cath Mummery, Professor of Clinical Neurology at the UCL Queen Square Institute of Neurology and Consultant Neurologist at University College London Hospitals NHS Foundation Trust. 'The magnitude of tau reduction and cognitive benefit observed in CELIA is among the most compelling reported to date in Alzheimer's disease drug development and supports advancing diranersen to Phase 3 development.'
As of this writing, Biogen shares are down 7% at $193.91.
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